Variable microwave phase shifter having moveable reactive stubs



Oct. 22, 1963 I J. F. REUVERS ETAL 3,108,237

VARIABLE MICROWAVE PHASE SHIFTER HAVING ubvmsw REACTIVE STUBS Filed Sept, 29, 1961 s Sheets-Sheet 1 Oct. 22, 1963 J. F. REUVERS ETAL 3,103,237 VARIABLE MICROWAVE PHASE SHIFTER HAVING MOVEABLE REACTIVE Filed Sept. 29, 1961 I "s Shegts-Sheet 2 Oct. 22, 1963 J F REUVERS ETAL 3,108,237

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United States Patent 3,108,237 VARIABLE MHJRQWA'VE PHASE SHlFTER HAVING MGVEABLE REACTIVE S'llJBS John F. Reuvers, Santa Ana, and James U. fllarlr, La

Habra, Callf., assignors to Hughes Aircraft Company,

Culver City, Calif., a corporation of Delaware Filed Sept. 2?, 1961, Ser. No. 142,458 2 Claims. (Cl. 333-311) This invention relates to a waveguide element and more particularly to a microwave phase shifter capable of being mechanically varied over a wide range of phase shifts without introducing objectionable standing wave ratios.

Adjustable phase shifters for waveguides are generally Well known in the microwave art. These prior art devices eifect phase shifts by means of movable dielectric vanes, movable sidewalls, line stretchers, and shunt slot Apparatus used to cfiect a phase shift in this manner, however, is generally complex, bulky, difiicult to retain in an operative condition or incapable of achieving controlled phase shifts over a wide range of frequencies.

dt is therefore an object of the present invention to provide an improved microwave phase shifter.

Another object of the present invention is to provide a microwave phase shifter capable of producing controlled phase shifts over a wide range of frequencies Still another object of the present invention is to provide a compact microwave phase shifter of comparatively simple construction.

A further object of the present invention is to provide a microwave device capable of being adjusted to produce a wide range of selected phase shifts without adversely affecting the standing wave ratio.

In accordance with the present invention, a conductive array of reactive stubs mounted on a beam is supported midway between the broad walls of a rectangular waveguide. A continuously variable phase shift is produced by moving the array of reactive stubs transversely between a side Wall and centerline of the waveguide by means of a drive screw. In addition to the foregoing, it is apparent that the conductive array of stubs of the present invention may be employed in a circular or elliptical waveguide when propagating an electromagnetic wave in the TE mode. Also, in that the reactive stubs are mounted symmetrically on the beam, it is preferable but not essential that the reactive stubs be in alignment with the electric field of the electromagnetic wave propagated by the waveguide.

The above-mentioned and other features and objects of this invention and the manner of obtaining them will become more apparent by reference to the following description taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is an isometric View, partially broken away, of a preferred embodiment of the invention;

FIG. 2 is an end view of the device of FIG. 1 partially broken away;

FIG. 3 is a top plan view of the device of FIG. 1 partially broken away;

FIGS. 4 and 5 are top and side views, respectively, of the conductive array of reactive stubs of the device of FIG. 1;

FIG. 6 is an isometric view, partially broken away, of an alternative embodiment of the invention;

FIG. 7 illustrates the phase shift characteristic of the device of FIG. 1;

FIG. 8 illustrates constant phase shift characteristics of the device of FIG. 1 for displacement versus frequency; and

FIG. 9 illustrates the standing wave ratio character istics of the device of FIG. 1.

Referring now to FIG. 1, a preferred embodiment of the present invention includes a mctfllic array 10 of reactive stubs '12 mounted on a beam 14. The beam 14 is, in turn, supported by rods 15, 16 intermediate the broad walls 17, 18 of a section of rectangular waveguide 20. Section of rectangular waveguide 20 additionally includes narrow walls 21, 22 and flanges 23, 24 for maintaining the section 20 in alignment with other lengths of similar waveguide, not shown.

Referring now to FIG. 2, the metallic array 10 of reactive stubs 12 is supported equidistantly between the broad sides .17, 18 of the section of rectangular Waveguide 20. The array 10 is centrally disposed intermediate the broad sides '17, 18 for convenience and may, for example, be disposed closer to one of the broad sides 17 or 18 than the other without materially affecting the operation of the device. Also, the beam 14 on which the metallic array 11) of reactive stubs 12 is mounted is slidably mounted on the transverse rods 15, 16. Referring to FIG. 3, the narrow walls 21, 22 of the section of rectangular waveguide 20 have protuberances 26, 27 and 28, 29 on the exterior sides thereof which are appropriately drilled and tapped for mounting the rods 15, 16 transversely across the section of rectangular wave guide 20. In addition, a threaded rod 30 is disposed transversely through a threaded hole in the beam 14 parallel to the rods 15, '16 and rotatably mounted in appropriately drilled holes in protuberances 31, 32 on the narrow walls 21, 22, respectively. A bearing 33. may be mounted intermediate the protuberance 32 and the threaded rod 30 if desired so that it may be more easily rotated. Lastly, the threaded rod 30 extends through the protuberance 32 in the narrow wall 22 of the section of rectangular waveguide 20 and is attached to a knob 34- thereby enabling the threaded rod 31 to be rotated and thus position the array 10 of reactive stubs -12 transversely within the section of rectangular waveguide 20. Rods 15, 16 and threaded rod 30 may be composed of either a dielectric material or metallic material and are preferably spaced of the order of onequanter guide wavelength apart.

Referring now to FIGS. 4 and 5 of the drawings, there are shown top and side views, respectively, of the array 10 of reactive stubs 12 mounted on the beam 1-4. The array 10 may be fabricated out of a single casting or piece of metal if desired. The reactive stubs 12 are arbitrary in number and progressively increase in height from the stub 12 located at the extremities of the beam 14 proceeding inwardly to the stubs mounted immediately adjacent the threaded rod 311. In addition, the stubs 12 are in general mounted substantially an odd multiple of one-quarter guide wavelengths apart on centers and, in particular, are mounted one-quarter guide wavelength apart on centers so as to minimize reflections. It is to be noted that the stubs 12 having the greater height shorten the wavelength within the section of rectangular waveguide 20 and, hence, are mounted closer together along beam 14. :In the event a S-band phase shifter is desired, an array 10 for use in rectangular waveguides of conventional dimensions (i.e., 1.000 x 2.840 inches) may have the dimensions shown in FIGS. 4 and 5. These dimensions would, of course, be changed proportionately to adapt the phase shifter to other ranges of frequency.

Referring now to FIG. 6, there is shown an alternate embodiment of the present invention which is similar to that of FIG. 1 with the exception that a section of circular waveguide 33 is utilized rather than the section of rectangular waveguide 20. In utilizing circular wave- 3 guide, it is generally desirable to induce the TE mode of propagation with the electrostatic field oriented parallel to the center lines through the reactive stubs 12, i.e., perpendicular to the beam 14.

In the operation of the device of the present invention, the reactive stubs 12 appear inductive in the vicinity of either of the side walls 21 or 22 of the section of rectangular waveguide 2d and produce a relative phase advance in a propagated plane wave relative to that which would occur with no phase shifter within the Waveguide. In the center region of rectangular waveguide 20, on the other hand, the stubs 12 of array 10 appear capacitive and cause a relative phase retardation in a propagated plane wave. Referring to FIG. 7, there is shown a characteristic 40- of the relative phase shift in degrees produced by the array 10 of FIGS. 4 and when placed in rectangular waveguide having cross-sectional dimensions of 1.000 x 2.840 inches. As shown in the drawing, there is a phase lag in excess of 150 when the array is positioned along the center line of the section of rectangular waveguide 20. As the array 10 is displaced from the center line by a distance of the order of 1.06, the phase lag decreases to zero. At this position, designated as point 41 on the characteristic 40, the array 10 is resonant and produces no net effect on the phase of a propagated plane wave through the rectangular waveguide 20. Further, as the array 10 is moved farther towards the side walls 21 or 22 of the section of rectangular waveguide 20, a phase lead is produced in a wave propagated by the rectangular waveguide 20. For the eight reactive stubs 12 illustrated having dimensions substantially as shown in FIGS. 4 and 5, a total phase shift of the order of 185 may be realized. creased or decreased by using a greater or lesser number of the reactive stubs 12, respectively.

Referring now to FIG. 8, there are shown various characteristics of the displacement of the array 10 from the center line of rectangular waveguide required to produce constant phase shifts from 0 to 180 throughout the S-band range of frequencies, i.e., from 2.5 to 3.4 kilomegacycles. In particular, a characteristic .2 shows the displacement required to produce 21 0 phase lag; a characteristic 43 shows the displacement required to produce a 45 phase lag; a characteristic 44 shows the displacement required to produce a 90 phase lag; a characteristic 45 shows the displacement required to produce a 135 phase lag; and a characteristic 46 shows the displacement required to produce a 180 phase lag. As is readily apparent from the characteristics 42 through 45, the variation in displacement of the array 10 required to produce a fixed phase lag is comparatively small for phase lags from 0 to 135 through the range of frequencies from 2.6 to 3.3 kilomegacycles. :It is apparent that a greater or lesser number of stubs .12 may be employed so that a selected range of phase shifts occurs with displacements similar to those of the characteristics 42 through 45.

The height, spacing and number of reactive stubs 12 included in the array 1% affect the reflected wave and hence the insertion loss incurred by placing the array 10 within the section of rectangular waveguide 20. Referring to FIG. 9 there is shown a contour diagram illustrating displacements of the array 10 with dimensions as shown in FIG. 4 which produce standing wave ratios in excess of 1.2 for the S-band range of frequencies. Displacements of the array 10 corresponding to standing wave ratios greater than 1.2 are illustrated by shaded The amount of phase shift may be inareas 50 in the contour diagram of FIG. 9. As is apparent from the contour plot of FIG. 9, the device of the present invention can be operated from 2.7 to 3.2 kilomegacycles to produce phase shifts from 45 to (see FIG. 8) without incurring a standing wave ratio greater than 1.20. It is apparent that numerous other combinations of heights and numbers of the reactive stubs 12 may be used to optimize this standing wave ratio throughout particular ranges of frequencies and/0r phase shifts.

Although the invention has been shown in connection with a certain specific embodiment, it will be readily apparent to those skilled in the art that various changes in form and arrangement of parts may be made to suit requirements without departing from the spirit and scope of the invention.

What is claimed is:

1. A phase shifting apparatus comprising a section of rectangular waveguide having first and second broad sides and first and second narrow sides; an elongated conductive member disposed parallel to and intermediate said first and second broad sides of said section of rectangular waveguide; a plurality of conductive cylindrical elements, each having an axis of rotation, disposed along said elongated conductive member at one-quarter guide wavelength intervals, said axis of rotation being normal to said first and second broad sides, said conductive cylindrical elements being disposed symmetrically about said elongated conductive member and said conductive cylindrical elements having progressively increasing lengths proceeding from the extremities of said elongated conductive member towards the center portion thereof; and means for maintaining said elongated conductive member at a selected transverse position intermediate said first and second narrow sides of said rectangular waveguide thereby to determine the phase shift of an electromagnetic wave propagated through said section of rectangular waveguide.

2. A phase shifting apparatus comprising a section of cylindrical waveguide of predetermined diameter and having a center axis; an elongated conductive member disposed Within said section of cylindrical waveguide and parallel to said center axis; a plurality of conductive cylindrical elements each having an axis of rotation disposed along said elongated conductive member at onequarter guide wavelength intervals, said axis of rotation being parallel and transverse to said cylindrical waveguide, said conductive cylindrical elements being disposed symmetrically about said elongated conductive member and said conductive cylindrical elements having progressively increasing lengths proceeding from the extremities of said elongated conductive member towards the center portion thereof; and means for maintaining said elongated conductive member at a selected transverse position along said predetermined diameter of said cylindrical waveguide thereby to determine the phase shift of an electromagnetic wave propagated through said section of cylindrical waveguide.

References Cited in the file of this patent UNITED STATES PATENTS 2,425,345 Ring Aug. 12, 1947 2,438,119 Fox Mar. 23, 1948 2,629,773 Hall Feb. 24, 1953 2,630,492 Muchmore Mar. 3, 1953 2,688,732 Kock Sept. 7, 1954 2,948,864 Miller Aug. 9, 1960 

1. A PHASE SHIFTING APPARATUS COMPRISING A SECTION OF RECTANGULAR WAVEGUIDE HAVING FIRST AND SECOND BROAD SIDES AND FIRST AND SECOND NARROW SIDES; AN ELONGATED CONDUCTIVE MEMBER DISPOSED PARALLEL TO AND INTERMEDIATE SAID FIRST AND SECOND BROAD SIDES OF SAID SECTION OF RECTANGULAR WAVEGUIDE; A PLURALITY OF CONDUCTIVE SYLINDRICAL ELEMENTS, EACH HAVING AN AXIS OF ROTATION, DISPOSED ALONG SAID ELONGATED CONDUCTIVE MEMBER AT ONE-QUARTER GUIDE WAVELENGTH INTERVALS, SAID AXIS OF ROTATION BEING NORMAL TO SAID FIRST AND SECOND BROAD SIDES, SAID CONDUCTIVE CYLINDRICAL ELEMENTS BEING DISPOSED SYMMETRICALLY ABOUT SAID ELONGATED CONDUCTIVE MEMBER AND SAID CONDUCTIVE CYLINDRICAL ELEMENTS HAVING PROGRESSIVELY INCREASING LENGTHS PROCEEDING FROM THE EXTREMITIES OF SAID ELONGATED CONDUCTIVE MEMBER TOWARDS THE CENTER PORTION THEREOF; AND MEANS FOR MAINTAINING SAID ELONGATED CONDUCTIVE MEMBER AT A SELECTED TRANSVERSE PORTION INTERMEDIATE SAID FIRST AND SECOND NARROW SIDES OF SAID RECTANGULAR WAVEGUIDE THEREBY TO DETERMINE THE PHASE SHIFT OF AN ELECTROMAGNETIC WAVE PROPAGATED THROUGH SAID SECTION OF RECTANGULAR WAVEGUIDE. 